This project is concerned with developing basic information on the ultrastructural morphology and properties of tooth enamel using transmission and scanning electron microscopy, microradiography, as well as other related physical methods. A special feature of the project is the capability of preparing thin sections of etched or fully calcified enamel for transmission electron microscopy from the same areas that are observed by scanning electron microscopy or microradiography. Objective are to obtain a precise and detailed body of information on the relation between structural organization and solubility properties. Three levels of enamel (surface, mid-region, and dentinoenamel junction) will be specifically studied in relation to solubility differences at the enamel crystal level. The development and maturation of the prism border area will be studied, particularly in deciduous as compared to permanent teeth. The correlated microradiographic-electron microscopic study of caries will be continuted. Effects of remineralizing solutions, with and without fluoride, on acid etched enamel thin sections will be examined at the ultrastructural level. This project will also extend to study sealant penetration into etched and incipient caries.